Study of Life

​I begin the second unit, the Study of Life, by asking students how they know if something is alive.  Depending on the class, some students will suggest that living things breathe, can move, and need water…but other students may know that living things are made of cells and can reproduce (shown in this video below).  We discuss some basic vocabulary and I give them the acronym RD GRENCH to help them with remembering some, but not all, life functions.  

I teach life functions by using examples:  plants, invertebrate animals, bacteria/monera (the term is still used in the NY State Curriculum), protista, and fungi.  I briefly discuss viruses and explain why they may or may not be considered “alive”.  I use supplementary lab and classwork assignments, as well as some videos of protists and invertebrates, to familiarize students with life functions shared among these organisms.​

​Once students have a working knowledge of life processes of some protists and invertebrates I bring the conversation back to cells and how they are studied. Many students remember microscope parts from having used them in middle school.  I briefly review the microscope parts to refresh their memories.  I show a mildly amusing video on the history of microscopes (scroll down for this) and students complete a classwork activity on the history of cell study.

After the discussion about microscopes and the history of cell study, I ask students to tell me the types of cells they have studied. Typically, students can tell some differences between plant and animal cells.  I explain that another way that scientists group cells is according to the presence of a nucleus.  I introduce the terms: "prokaryote" and "eukaryote".  After explaining the terms and giving a brief overview of the Theory of Endosymbiosis, I show a short video about early earth (found below).  I conclude the lesson by mentioning some of the cell structures found in eukaryotic cells...which we will cover in more depth in a later class. ​

Class discussions about the types of cells, relative sizes of cells, and generalized organelles in cells logically leads to the Compound Microscope LAB.  In the lab, they familiarize themselves with the orientation of specimens in the field of view by comparison to "real life". Students note that specimens in the field of view appear larger, are backwards, and upside down compared to their actual position on the microscope stage.  They also learn about microscopic measurement.

​I use the examples of facial muscles being rendered unable to receive neural messages after Botox injections and taste buds being rendered unable to detect sweetness after using toothpaste when I discuss receptor molecules on cell membranes.

​Finally, I review transport of molecules across the cell membrane by offering students various scenarios such as a human blood cell in solutions of varying salinity and descriptions of amoeba in a freshwater environment.

​Following discussions of the cell membrane, we then turn our attention to structures within the membrane.  Beyond notes, I use diagrams, assignments, and videos to assist students in learning cell organelles.  Many can be found in TEACHING RESOURCES.  As we discuss organelles, I note several points of divergence between plant and animal cell parts.  During a lab investigation, students examine onion cells, elodea leaf cells, and cheek cells to learn to differentiate between plant and animal cells.

Next, I turn the attention of the class to the cell membrane.  I discuss the fluid mosaic, the bi-lipid layer, protein channels, carbohydrate chains, and receptor molecules.  I also describe diffusion, osmosis, facilitated diffusion, and active transport.  

In "The Egg Lab" students investigate the movement of water molecules across the membrane of a raw egg to demonstrate what happens in microscopic cells.  As a follow-up, the New York State Lab, has a diffusion of food coloring component, an artificial cell component, and an examination of red onion cells exposed to both fresh water and saline solution.  Students are exposed to many examples of diffusion across biological membranes.

In describing passive and active transport, I compare those processes to riding a bicycle up or down a hill, respectively.  I explain that riding a bike down a hill does not require pumping the pedals (no energy is required); by contrast pumping (energy) is necessary in riding the bike up the hill.  In this way, passive transport is like riding a bike "from an area of high concentration to an area of low concentration", whereas active transport is pumping/riding a bike "from an area of low concentration to an area of high concentration."​

The Presentation and Student Notes files are available here.